Split array into two arrays by index even or odd

Use array_filter (PHP >= 5.6):

$odd = array_filter($array, function ($input) {return $input & 1;}, ARRAY_FILTER_USE_KEY);
$even = array_filter($array, function ($input) {return !($input & 1);}, ARRAY_FILTER_USE_KEY);

As an almost-one-liner, I think this will be my favourite:

$even = $odd = array();
foreach( $array as $k => $v )  $k % 2  ?  $odd[] = $v  :  $even[] = $v;

Or for a tiny little more? speed:

$even = $odd = array();
foreach( $array as $k => $v )  ( $k & 1 ) === 0  ?  $even[] = $v  :  $odd[] = $v;

A bit more verbose variant:

$both = array( array(), array() );
// or, if $array has at least two elements:
$both = array();

foreach( $array as $k => $v )  $both[ $k % 2 ][] = $v;
list( $even, $odd ) = $both;

With array_chunk:

$even = $odd = array();
foreach( array_chunk( $array, 2 ) as $chunk ){
  list( $even[], $odd[] ) = isset( $chunk[1]) ? $chunk : $chunk + array( null, null );
  // or, to force even and odd arrays to have the same count:
  list( $even[], $odd[] ) = $chunk + array( null, null );
}

If $array is guaranteed to have even number of elements:

$even = $odd = array();
foreach( array_chunk( $array, 2 ) as $chunk )
  list( $even[], $odd[] ) = $chunk;

PHP 5.5.0+ with array_column:

$chunks = array_chunk( $array, 2 );
$even = array_column( $chunks, 0 );
$odd  = array_column( $chunks, 1 );

Something similar for older PHP versions. The keys will be 0,2,4,… and 1,3,5,…. If you don't like this, apply an array_values too:

$even = array_intersect_key( $array, array_flip( range( 0, count( $array ), 2 )));
$odd  = array_intersect_key( $array, array_flip( range( 1, count( $array ), 2 )));

or

$even = array_intersect_key( $array, array_fill_keys( range( 0, count( $array ), 2 ), null ));
$odd  = array_intersect_key( $array, array_fill_keys( range( 1, count( $array ), 2 ), null ));

I am not sure if this is the most elegant way, but it should work a charm:

$odd=array();
$even=array();
$count=1;
foreach($array as $val)
{
    if($count%2==1)
    {
        $odd[]=$val;
    }
    else
    {
        $even[]=$val;
    }
    $count++;
}

One more functional solution with array_chunk and array_map. The last line removes empty item from the 2nd array, when size of a source array is odd

list($odd, $even) = array_map(null, ...array_chunk($ar,2));
if(count($ar) % 2) array_pop($even);

Just loop though them and check if the key is even or odd:

$odd = array();
$even = array();
foreach( $array as $key => $value ) {
    if( 0 === $key%2) { //Even
        $even[] = $value;
    }
    else {
        $odd[] = $value;
    }
}

One

$odd = $even = array();
for ($i = 0, $l = count($array ); $i < $l;) { // Notice how we increment $i each time we use it below, by two in total
    $even[] = $array[$i++];
    if($i < $l)
    {
       $odd[] = $array[$i++];
    }
}

Two

$odd = $even = array();
foreach (array_chunk($array , 2) as $chunk) {
    $even[] = $chunk[0];
    if(!empty( $chunk[1]))
    {
       $odd[] = $chunk[1];
    }
}

Based on @Jon's second variant, I made this following for use with PHP Smarty v3 template engine. This is for displaying news/blog with both one or two columns template model.

After the MySql query I'll do the following code :

if(sizeof($results) > 0) {
    $data = array();
    foreach($results as $k => $res) {
        if($k % 2 == 0) {
            $res["class"] = "even";
            $data["all"][] = $data["even"][] = $res;
        }
        else {
            $res["class"] = "odd";
            $data["all"][] = $data["odd"][] = $res;
        }
    }
}

I obtain an array of 3 sub-arrays (including odd/even class) with Smarty syntax of use :

1. all items {foreach $data.all as $article}...{/foreach}
2. odd items only {foreach $data.odd as $article}...{/foreach}
3. even items only {foreach $data.even as $article}...{/foreach}

Hope it helps some people...

$odd = [];
$even = [];
while (count($arr)) {
    $odd[] = array_shift($arr);
    $even[] = array_shift($arr);
}

    <?php

$array1 = array(0,1,2,3,4,5,6,7,8,9);
$oddarray = array();
$evenarray = array();

$count = 1;

echo "Original: ";
foreach ($array1 as $value)
 {
    echo "$value";
}

echo "<br> Even: ";

foreach ($array1 as $print) 
{
    if ($count%2==1) 
    {
        $evenarray = $print;
        echo "$print";
    }
    $count++;
}

echo "<br> Odd: ";

foreach ($array1 as $print2) {
    if ($count%2!=1) 
    {
        $oddarray[] = $print2;
        echo "$print2";
    }
    $count++;
}

?>

Output:

Original: 0123456789
Even: 02468
Odd: 13579